Sway Bar facts

Discussion in 'Modifications & DIY how-to' started by jt money, Mar 8, 2006.

  1. jt money

    jt money 350hp mmm mmm Good! Supporting Member

    Sway Bar basics

    Sway Bars

    Controling body motions and weight transfer
    Sway bars or Stabilizer bars control the vehicle's body roll or lean during a corner. What that means is that sway bars can have a large effect on "weight transfer" and a tire's "contact patch". Hence, oversteer or understeer can be produced/controlled by adjusting/changing the front/rear sway bars.

    Through the just the use of sway bars alone, we have seen increases in grip from .03 - .10 g's...pretty significant!
    Rear Sway Bar

    One of the ways that Subaru (and most other auto manufacturers) make sure some bone head isn't going to sue them is they dial understeer into the chassis handling dynamics. A more balanced car (or one with a nice little bit of slight oversteer) can be had by installing a larger, thicker (read stiffer) rear sway bar (checkout the picture below of the whiteline vs stock sway bars). By changing out the stock (20 mm) rear sway bar with a thicker (22+ mm...and hopefully adjustable too), you increase the rear end's resistance to roll. This helps to transfer weight to the front outside tire during a corner...thus increasing the front end's grip. That is why everyone says to tighten up the rear end to reduce understeer.
    What happens when you stiffen the rear end is that the weight that would be transfered from the rear inside wheel to the rear outside wheel is tranferred diagonally to the front outside wheel. With the stiffened rear end the sway helps resist body roll and full weight transfer to the rear outside wheel.

    Just remember that if you stiffen the rear end, you will have less warning when you reach the tires limit of adhesion and will have "less warning" before the car oversteers. From our experience, even at the stiffest setting (the inside hole is the stiffest setting) the WRX with the factory suspension does not exhibit dangerous snap oversteer in low to medium turns.
    General Sway Bar Setup Rule

    For a more balanced car, the general rule (from stock settings) is that you need to decrease the rear grip and increase the front grip (relatively speaking) to the rear. In other words, it is best to increase grip both front and back...but you should increase the front grip (in the stock setup) more relative to the rear.
    Front Sway Bar
    Should you just change out the rear sway bar? If you leave the front stock sway bar (17 mm) and just replace the rear, you are missing quicker turn in and other benefits from the front sway bar. Upgrading to a 22 mm front sway bar seems to provide the best results. Remember not to change out the front sway bar without changing the rear (unless you want to increase understeer :^(.
    Stiffer (urethane) bushings

    Because they are much stiffer than the stock rubber bushings, Urethane Bushings quicken the response of the sway bar.

    Urethane Bushings also increase NVH (Noise, Vibration, & Harshness)...making your ride a little stiffer and louder.
    Most Sway Bars (like Whiteline) come with Urethane Bushings included. Note that unless the bushings are well lubricated, they will squeak.
    Nylon Links

    The rear sway bars are actually connected to the lower control arm via a nylon link. These links tend to flex slightly and can be changed out in favor of stiffer, urethane links. The stiffer links do not stiffen or tighten up the rear end more...what they do is decrease the response time for the sway bars to do their job. A relatively inexpensive and worthwhile upgrade.
    Below is the Perrin Solid Sway Bar Link.

    *thanks for Scoobytuner for this artical.
    Last edited: Mar 8, 2006
  2. rolling_trip

    rolling_trip Active Member

    great post, thanks for breaking it down there JT
  3. MarkM2016GTI

    MarkM2016GTI Supporting Member

    Thanks JT for another fine article!!!.
    Very Helpful!!!.

  4. sol drums

    sol drums Active Member

    thanks jt!
  5. miloman

    miloman Retired Admin

    thanks JT
  6. Superdude

    Superdude Active Member

    help me understand, please. i've read this piece of advise and both make total sence to me.
    "There are... things you can do to your car in a stock class to combat understeer, atleast that i have found helpful. Larger front sway bar will definately give you faster turn in and make your rear a bit more squirelly."
    i'm not judging any of this, just trying to get a full understanding, that's all.
  7. jt money

    jt money 350hp mmm mmm Good! Supporting Member

    heres some more sway bar info that i hope can help you

    Normally, without a sway bar when the car corners the weight of the chassis
    shifts toward the outside of the turn compressing the springs on that side. The
    springs on the inside generally extend a little, or do nothing. Relatively to the
    chassis itself, it appears that the outside suspension compresses and the inside doesn't.

    A sway bar couples the suspensions on each side to each other, *AND* relative
    to the chassis. If you could put the car up on a lift and actually compress
    the suspension on one side by hand, then a sway bar makes the compression of one
    side also try to compress the suspension on the other. Ok.. it's still not
    really obvious why that's useful so I'll say the same thing a different way.

    A sway bar effectively increases the spring rate on whichever side
    is compressed the MOST. If the sway bar were absolutely solid with no
    twist so there's a 100% coupling between each side then
    an attempt to compress one spring actually becomes an attempt to
    compress both springs. It doubles the spring rate. If the bar has some
    twist, then it may only increase the spring rate by say 50% on whichever side
    is compressed the most.

    So you're driving down the road and you go over
    a bump that goes across the entire lane. The sway bar
    does nothing. Both sides compress normally. You go around a
    corner and the chassis starts to lean and compress the outside
    suspension and now it's as though you have a bigger spring
    out there, so the car remains more level. That's the good part.
    Here's the bad part. You hit a bump with only one side, and it
    behaves the same way, as though you have a stiffer spring,
    so you feel uneven bumps more. You feel it crossing anything
    diagonally as well, such as coming into or out of a parking lot
    or driveway curb.

    That's all the simple "How does a sway bar work?" part.
    The real tricky one is.. "What does a sway bar do?"
    1. We know it keeps the car more level. So what? Limiting the lean of
    the body is good because it means that when you take a quick set into
    a turn, that the body isn't still moving sideways after the tires at their
    limits. Otherwise you turn in quickly, the tires grip, then the body finally finishes
    leaning, when it stops, the tires loose grip. This is especially noticable in most
    cars in the slalom where you lean one way then the other and so forth.

    2. It limits camber changes. The camber is the angle that the tire leans in or out at the top
    relative to the chassis of the car. The camber directly impacts the angle at which the tire
    cross section meets the road and thus controls lateral grip. As the suspension compresses
    the camber angle generally changes relative to the chassis. With a normal Macpherson
    strut that hasn't been lowered, the camber goes from positive to more negative as the
    lower A arm swings out straight, and then back to positive as it swings up. That swing
    up into positive camber is BAD. At that point the chassis is already leaned over so the
    tire may be starting to roll onto its sidewall. Changing the camber even more positive
    just just nasty. A big sway bar will prevent the body roll in the first place, and
    prevent the suspension compression on the outside which causes the positive camber
    change relative to the chassis.

    3. Transfer lateral grip from one end of the car to the other.
    This one is a real trick to understand, but racers exploit this EVERY time they go
    on the track. Their spring rates are often so high, the cars so low, and their
    suspension travel so little, that the whole camber and body lean problem is already
    a non-issue. The car doesn't lean much with 500 lb springs. They use their bars
    to change the balance of the car. Here's the simple rules first.
    A big bar on the front, increases rear lateral and motive traction.
    A big bar on the rear, increases front lateral and motive traction.
    The applications. If the car is understeering, decrease front bar size, or increase
    rear bar size. This increases front lateral grip and decreases rear lateral grip
    giving the car a more neutral to oversteer feel. Reverse the process for
    too much oversteer.
    I mentioned motive grip. That's the neat one. Let's say your RWD car is handling ok, but
    everytime you get into a corner hard and get on the gas the rear inside tire breaks loose
    and spins. You can't accelerate out of the turn. You can go around the turn quite
    quickly, but you can't accelerate out, and the guy with traction hooks up and
    passes you halfway down the next straight because he came out of the turn going 3-4mph faster.
    The reason you're losing the traction at the inside rear, is usually because the rear bar is too big.
    As the rear outside suspension compresses, it's actually causing the rear inside suspension to
    compress as well (because the bar couples the sides.. remember where we started), and that
    decreases the weight on the rear inside tire.
    First thing. Decrease size of rear bar. That decouples the sides a bit, let's the inside tire press
    down on the road more and thus not spin when you're on the gas.

    Here's where it gets really tricky.
    If decreasing the size of the rear bar doesn't help enough the next thing you do is
    increase the size of the front bar. When the outside front compresses in a corner, it
    causes the inside front to compress and may actually lift that tire completely off the
    ground. The car is now sitting on 3 tires and guess where the weight that was on
    the inside front goes? Outside front? Some of it. The rest goes to the inside rear
    where we need more grip. The total weight of the car hasn't changed. It's just been
    redistributed, and a sway bar at one end, actually transfered weight to the other
    end of the car. Here it is in action on a AWD car
    See the inside front tire off the ground. That translates into more motive grip
    at the rear, and thus more acceleration, and believe me, that car rockets
    out of corners.
    *thanks to Daemon42 of vwvortex for the artical.
    *thanks to javid for the use of his picture.
    Last edited: Mar 9, 2006
  8. Superdude

    Superdude Active Member

    very well said, JT. Thanks.
    is this why the SCCA allows a front sway and not a rear for the stock class? because the rear makes that much more of a difference over the front?
  9. jt money

    jt money 350hp mmm mmm Good! Supporting Member

    yes the rear bar increases the motive traction in the front among other things.
  10. moose

    moose Infina Mooooooose!

    The guy who did that writeup has a lot of other good information too. I remember when he first posted it on VWvortex (we have a Jetta too), and it's cool to see it's still making the rounds.


    His page on differentials is pretty damn neat:
    Last edited by a moderator: Mar 9, 2006
  11. sol drums

    sol drums Active Member

    nice find moose...

    if you guys find more post em up. my mind is loving all the new info! :bigthumb:
  12. jt money

    jt money 350hp mmm mmm Good! Supporting Member

    this is where i got the write up from
    i added a suby pic insted of a bmw cause it shows the same thing.
    looks like the same guy but i didnt see his info on this page. do you know his name so i can edit a credit where its due. thanks

    edit i footnoted a thanks to his screen name from vwvortex. also i want to reinerate i was in no way shape or form tring to imply that i was the one writing these articals. i footnoted all the other articals. thanks for bringing it to my attention that i forgot one. :)
    Last edited: Mar 10, 2006
  13. jayj713

    jayj713 Member

    Quick question will 02-05 wrx sway bars fit on an 06 wrx?
  14. jt money

    jt money 350hp mmm mmm Good! Supporting Member

    cobb and perrin both do. i dont see why the rest wouldnt be the same.
  15. Bolderer

    Bolderer Member

    Excellent writeup. Thanks.
  16. FACE

    FACE Active Member

    This is my first post here and I thank you kindly for all the helpful info! I am trying to decide what my next mod on my 06 sti will be and Im thinking sway bars after reading this and becoming more educated about them.
    Thanks again!!!
  17. Alex

    Alex Community Founder Staff Member

    Swaybars are always a good choice!
  18. bluetwo

    bluetwo Active Member

    I vow to never own another vehicle without upgrading the sways. Unless of course the car handles like an S2000 out of the box or something. In my mind you could make nearly any vehicle handle and feel much better with this easy upgrade.
  19. nsvwrx

    nsvwrx Active Member



    26mm front and 24 mm rear will cut your total roll angle (at the same cornering force) in *HALF.* You will IMMEDIATELY notice the improvement. The cars will all pull between 0.9 and 1.0 G's laterally. Even mildly cornering, at say 0.5-0.6 G's, the reduced roll rate, and resulting improvement in handling limit and confidence are HUGELY apparent.

    Even if you are going to run SCCA stock class, the front bar is open.

    Yes, "USUALLY" stiffer bars equal less grip. In the rear of almost every car out there, stiffer rear bars will promote rotation - i.e. less grip in the rear.

    Sometimes, and DEFINITELY on the Impreza's a *BIGGER* front bar will *REDUCE* understeer and *INCREASE* overall grip. Anything that improves overall grip, *AND* improves balance (understeer / oversteer) is a GREAT mod.

    Most likely the reason that front grip improves so well with stiffer front bars is that the camber and toe curves of our Macpherson struts are so bad that reducing roll-induced alignment losses more than offsets the increase in load on the tire.

    We have gone as big as 27-29mm adjustable front sway bars. They are still reducing understeer and improving overall grip. The 27mm bar is the biggest bar that will fit into the stock mounts, it actually necks down to go through the mounts. Some auto-crossers, in classes where it's legal, have had bigger bars and mounts custom made.

    The only time I would say that this is getting toward too much front bar is with 670 pound front springs, in the *WET* the 27mm felt like it might be too little roll for optimum handling. If you are going over 600 pound front springs, you may want to stay with the 24-26mm adjustable front, so you can go down in the wet.

    My favorite bars for most people are the 24-26mm adjustable front bar and the 22-26mm adjustable rear. The 27-29 has had a few fitment issues, which should be resolved soon, then I'll probably go back to suggesting that front bar. I believe the 22-26 rear is the biggest mass-produced rear bar.

    Somewhere in the 26-29mm front and 24-26mm rear setting will almost always be ideal.

    The nice things about sway bars is that they have VERY little negative effect on ride-quality. The only time you'll really notice them negatively is dropping off a ledge, like turning in or out of parking lots and driveways.

    So.. as SS says.. getting only a FSB WOULDN'T get you more understeer as this article states.
  20. BrianGT

    BrianGT Banned

    I love our 32mm front bar and stock rear bar. Once we get coilovers, we will try running no rear bar, and a smaller front bar.

    I am not a fan of big rear bars, as once you lift a rear wheel, all goes to shit.
  21. clemsonscooby

    clemsonscooby Active Member

    Good write up JT. I am also running the 32mm Strano and it has made the biggest difference yet in my cornering ability. I ran the rear only 26mm for a while due to the 03's smaller rear bar than other models (17mm). It worked well but caused a lot of rotation in the rear, but did not always transition into faster cornering. It was nice being able to get the car turned around for sharp 180's, but did nothing for slaloms and long sweepers.

    This weekend was the first time I ran the strano 32mm in the dry and what a difference it made. The tires tell the whole story. Before the bar I was wearing a lot of the outside edge of my front tires. This was due to hard cornering my tire was rolling on itself and making my alignment mean nothing. Now, I noticed the tire wear was almost uniform across the wheel with a -2.5 camber setting up front. This increased the speed at which I can corner and will make my tires last a lot longer.

  22. WRBlue48

    WRBlue48 New Member

    YA so the stiffest setting is as shown in the original pic with the perrin endlink correct?
  23. Koolaid

    Koolaid Member

    Bigger the better
  24. aftercrash

    aftercrash Member

    :naughty:girlfriend says the same thing
  25. easterbran

    easterbran Member

    Great info, thanks!
  26. subie4life

    subie4life New Member

    thanks JT! now that i truly understand the whole concept i can go ahead and buy some sways for my car.
  27. LoamRanger

    LoamRanger New Member

    Great info, thanks!

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